In a typical push-in type lamp unit used in decorative light sets a bulb is mounted in a plastic lamp base and has a pair of lead wires which extend through the bottom of the lamp base and double back over opposite outer side faces of a plug-in portion of the lamp base. The lamp base plugs into a socket in a lamp holder presenting contact elements at opposite sides which are engaged by the lead wires from the bulb. The contact elements in turn engage insulated wires which may be presented by a single cord as shown, for example, in Pat. No. 4,779,177. Preferably the plug-in portion of the lamp base and the socket in the lamp holder are shaped so that the lamp base must be properly oriented for proper lead wire to contact element engagement in order for the plug-in portion to be pushed into the socket. Commonly decorative reflectors surround the bulb and have tubular extensions which are sleeved with a friction fit on the lamp holder.
Sometimes the plug-in portion of the lamp base in a plug-in light assembly works loose from the lamp holder socket sufficiently to break electrical contact between the bulb leads and the contact elements in the lamp holder, and sometimes the associated reflector unit comes loose from the lamp holder. Such can occur, for example, during packing and shipping, or while the light set is being handled while being mounted in a decorating position or removed therefrom for storage.
Although a relatively snug fit between the lamp base and the lamp holder is preferred to maintain electrical contact between the bulb leads and the contact elements, it is also preferred to have the lamp bases relatively easy to remove for bulb replacement in case of bulb failure. Accordingly, there has been a need for a practical, effective lock-on system to prevent unintentional dislodgement of the lamp bases and reflectors from the lamp holders of plug-in type decorative light units, but which can both be easily manually released for bulb replacement. Since the lamp bases, lamp holders, and reflectors are normally plastic injection-molded parts, a solution to the lamp loosening and reflector loosening problem is not practical if it unduly complicates the molding process or assembly of the sets.